The present invention relates to new cathodes which can be used in electrolysis. It also relates to a process for the manufacture of such cathodes. It relates especially to cathodes which can be used for the electrolysis of an aqueous solution of an alkali metal halide which is especially remarkable because of the low value of its working potential and the stability of its electrochemical performance with time.
These cathodes belong to the group of activated metal cathodes obtained by coating a cathode substrate by means of various activating materials, the purpose being essentially to reduce the hydrogen overvoltage in an alkaline medium. One of the techniques which can be used; generally known as "high area nickel", consists in forming a coating of microporous nickel on a ferrous substrate by first depositing a nickel-zinc alloy and then removing the zinc. Other techniques consist in depositing certain metal alloys such as nickelmolybdenum alloys (British Patent No. 922,350) on the substrate.
European Patent Application No. 0,129,734 describes cathodes bearing a coating consisting of a mixture of at least one platinum group metal and at least one oxide of a metal of the metal group, the platinum group metal representing 2 to 30% of the weight of the said mixture. Japanese Patent Application published under No. 7/13,189 describes a nickel or nickel alloy cathode bearing a coating consisting of a platinum group metal or an oxide of the said metal.
British Patent No. 1,511,719 describes a cathode comprising a metal substrate, a cobalt coating and a second coating of ruthenium.
U.S. Pat. No. 4,100,049 describes a cathode comprising a substrate and a coating consisting of a mixture of a precious metal oxide and of an oxide of a valve metal, especially zirconium oxide.
Japanese Patent Application published under number 090,080 describes a technique for the manufacture of a cathode consisting in treating a ferrous substrate with perchloric acid and then coating this cathode by sintering active substances comprising ruthenium, iridium, iron and nickel in the form of a metal or a metal compound.
A technique for depositing a coating consisting of a nickel-palladium alloy onto a substrate consisting, for example, of nickel is also described in U.S. Pat. No. 3,216,919. According to this patent, a layer of alloy is applied in powder form to the substrate and then sintering of the said alloy powder is carried out.
Coating of an electrode by electrodeposition of ruthenium-nickel alloy has also been proposed (Russian Pat. No. 264,096).
Japanese Patent Application published under number 110,983 (U.S. Pat. No. 4,465,580) describes a cathode bearing a coating consisting of a dispersion of particles of nickel or of a nickel alloy and an activator consisting of platinum, ruthenium, iridium, rhodium, palladium or osmium or of an oxide of these metals.
Japanese Patent Application published under number 53/010,036 describes a cathode which has a valve metal substrate and a coating of an alloy of at least one platinum group metal and a valve metal and, if appropriate, a surface coating of at least one platinum group metal.